Hi,

This animation does not look good at all to me. The cone seems to have gone 
through the granular bed with no resistance at all, and the granular bed 
did not seem to respond to this impacting object. Also, if you monitored 
the cone force, I suspect you just got an extremely small reading. Do you 
agree? I would like to ask you to do one thing: could you pull from the 
*develop* branch of Chrono (newest commit), then build and run your script 
again with it? This is because there was a bug in granular module that 
could potentially disable mesh--particle contact unexpectedly, if you used 
an older version. I do not think it is very likely that your simulation 
suffered from this bug, but let's rule out this possibility first.

After that, the task is to make this simulation physical. I believe the "no 
contact pair when Young's modulus is below particular value" is just the 
by-product of some unphysical phenomenon, such as huge penetration, super 
large angular velocity, failure to detect contacts etc. And you have to 
debug based off a "minimal" run that is physical. To be physical, it has to 
look right at least... In your case, you have to find a test scenario where 
it runs without errors, and the mesh and particles seem to interact with 
each other normally (cone punches a crater on the granular bed).

By the way, we still cannot run your script because there is no JSON file 
attached. On top of that, I am sorry that I currently do not have time to 
run or debug it even with the JSON file. But maybe I can read it to get a 
brief idea. I also think this post discussing the general question-asking 
practice <https://stackoverflow.com/help/how-to-ask> can be useful to 
consider.

Thank you!
Ruochun

On Saturday, July 2, 2022 at 4:27:13 PM UTC-5 [email protected] wrote:

> Hello,
>
> I have implemented one body and included the two meshes there. However, 
> the results I got did not match what I expected where the forces were not 
> producing the stress values that I was expecting on the tip of the cone. As 
> a result, I decided to switch back to my old method and see what 
> differences I get. I am only using three of the four bodies that are 
> created (I should probably comment on the one that I am not using out). One 
> of the three bodies is used as a guide for the motor. Also, I assumed that 
> both implementations would generate the same results since I am basically 
> trying to do the same thing in two different ways. However, I get 
> completely different results as well. I have animated the results for a 
> specific young modulus value and everything looks good when animated. 
> However, the physics is still different for both implementations. I am 
> including the animation of the file that I attached earlier as well as the 
> meshes I used and my other implementation for one body.  
>
>
> Thank you, 
> Mohammad
> On Thursday, June 30, 2022 at 12:09:35 AM UTC-7 Ruochun Zhang wrote:
>
>> Hi,
>>
>> Did you visualize your simulation? I doubt if this script can produce the 
>> correct physics. Last time, I stated that I believed one Chrono body was 
>> enough, and you had to collect force from both pieces of your meshes. This 
>> script uses at least 4 ChBodies (it may work, but I do not understand how 
>> they are used here) and seems the force is collected from the tip mesh 
>> only. Again, that's my speculation, because I don't know the mesh you used; 
>> but I doubt it would work, with low *or* high Young's modulus. It may 
>> happen to not throw an error at certain settings.
>>
>> Perhaps more importantly, I know the tip force is what you are after but 
>> did you manage to get a one-mesh-one-cone test scenario running, visualize 
>> it and validate the physics it produces? I think you have to start there, 
>> and if you have that the rest should follow naturally.
>>
>> Thank you,
>> Ruochun
>>
>> On Thursday, June 30, 2022 at 12:07:59 AM UTC-5 [email protected] 
>> wrote:
>>
>>>   Hi,
>>>
>>> I am trying to use the Chrono gpu to achieve a similar effect as the run 
>>> a cone penetration test but have been running into some difficulties. I 
>>> hope that somebody here would be able to help me out.
>>>
>>> When setting the young's modulus for the particles and boundaries to 
>>> 1e9, I get the following error:
>>>
>>>    - No available contact pair slots for body xxxxx and body xxxxx
>>>
>>> However, when I run the simulation with values larger than 1e9, the 
>>> simulation runs smoothly. 
>>>
>>> It seems strange to me that there seems to exist a critical value of 
>>> cohesion that causes models to behave in unexpected ways. I am wondering if 
>>> anybody here has had success with using low values for young's modulus in 
>>> Chrono GPU. I am attaching my file for your reference. 
>>>
>>>

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